1. Field of the Invention
The present invention relates to a semiconductor device controlling an electrostatic actuator using MEMS (Micro Electro Mechanical Systems) and to a method of controlling the electrostatic actuator.
2. Description of the Prior Art
Attention is paid to MEMS as one of technologies for reducing the size, weight, and power consumption of recent electronic equipment and for sophisticating the function thereof. The MEMS is a system in which a minute mechanical element is combined with an electronic circuit element by a silicon process technology.
U.S. Pat. No. 5,578,976, for example, discloses a structure of an electrostatic actuator using the MEMS technology. To place an electrostatic actuator in a closed state (state in which an upper electrode is in contact with a lower electrode through an insulation film), a potential difference is applied between the upper electrode and the lower electrode so that electrostatic attraction between the electrodes exceeds the elastic force of a movable portion to which the upper electrode is fixed.
In the electrostatic actuator in the closed state as described above, since the upper electrode is in contact with the lower electrode through the insulation film, the capacitance between the upper electrode and the lower electrode is larger than that when the electrostatic actuator is placed in an open state. At the time, a charge may be injected into the insulation film and the insulation film may be trapped by the FN (Fowler-Nordheim) tunnel or the Pool-Frenkel mechanism. This phenomenon is called dielectric charging of an electrostatic actuator.
When the amount of charge trapped by the insulation film by the dielectric charging is set to a value larger than a certain value, even if the potential difference between the upper electrode and the lower electrode is set to 0 V, since the upper electrode is attracted to the charge in the insulation film, the electrostatic actuator can not be shifted from the closed state to the open state. This phenomenon is called stiction due to the dielectric charging.
Although a means for avoiding the stiction is also disclosed in, for example, Non-Patent Document 1, G. M. Rebeiz, “RF MEMS Theory, Design, and Technology, “Wiley-Interscience, 2003, pp, 190-191, it is difficult to completely eliminate the amount of charge trapped by an insulation film and to completely excluding charging. Accordingly, there is desired a semiconductor device which can simply and accurately determine a state of an electrostatic actuator including whether or not charging is generated and which promptly restores to a normal operation state when it is determined that the charging and the like are generated to the electrostatic actuator.